原位矿化羟基磷灰石/高密度聚乙烯纳米复合材料的颗粒增强机制研究

通过SEM，AFM，XRD等检测手段对原位矿化复合方式制备的羟基磷灰石，高密度聚乙烯（HAP／HDPE）材料的显微结构进行了系统研究。研究表明，原位矿化复合方式制备的HAP／HDPE材料中，HAP颗粒以纳米尺度均匀分散在HDPE基体中，且与HDPE以化学键的方式结合。这种高的界面结合强度使HDPE结晶度提高，HDPE在HAP颗粒表面取向结晶，并且诱导HDPE形成高度取向的纤维结构。另一方面，HAP颗粒在对HDPE具有成核作用，纳米HAP颗粒的均匀分散使得HDPE在HAP质量含量相同情况下能形成更多的晶核，从而使HDPE的晶粒细化，这两方面的原因导致材料在保证高强度和高模量的情况下具有高的断裂韧性。     

Evaluation of mechanical and thermal properties of Poly (butylene terephthalate) (PBT) composites reinforced with wollastonite

Particulate filled polymer composites are becoming attractive because of their wide applications and low cost. Present study deals with the preparation and characterization of PBT/wollastomte composites and analyzing the effect of incorporation of varying concentration of wollastonite on the mechanical, thermal, and morphological properties of PBT thermoplastic composite for future industrial applications. In the composites wollastonite content was varied by 0–30 % by weight. Tensile strength exhibited a marginal increase whereas a dramatic increase was observed in modulus with an increase in filler content. The experimental results were also compared with theoretical predictions which revealed good level of interfacial interaction in the composites. Thermal analysis revealed an increase in percent crystallinity and also the onset crystallization temperature thereby indicating the nucleating efficiency of wollastonite. Study of the fracture surface by SEM revealed a change in the micromechanical deformation process with an increase in filler content.     

Processing,microstructure, and mechanical behavior of cast magnesium metal matrix composites

Magnesium metal matrix composites (MMCs) have been receiving attention in recent years as an attractive choice for aerospace and automotive applications because of their low density and superior specific properties. This article presents a liquid mixing and casting process that can be used to produce SiC particulate-reinforced magnesium metal matrix composites via conventional foundry processes. Microstructural features, such as SiC particle distribution, grain refinement, and particle/matrix interfacial reactions of the cast magnesium matrix composites, are investigated, and the effects of solidification-process parameters and matrix alloys (pure Mg and Mg-9 pct Al-1 pct Zn alloy AZ91) on the microstructure are established. The results of this work suggest that in the solidification processing of MMCs, it is important to optimize the process parameters both to avoid excessive interfacial reactions and simultaneously achieve wetting, so that a good particle distribution and interfacial bonding are obtained. The tensile properties, strain hardening, and fracture behavior of the AZ91/SiC composites are also studied and the results are compared with those of the unreinforced AZ91 alloy. The strengthening mechanisms for AZ91/SiC composite, based on the proposed SiC particle/matrix interaction during deformation, are used to explain the increased yield strength and elastic modulus of the composite over the magnesium matrix alloy. The low ductility found in the composites is due to the early appearance of localized damages, such as particle cracking, matrix cracking, and occasionally interface debonding, in the fracture process of the composite.     

Influences of matrix ductility,interfacial bonding strength,and fiber volume fraction on tensile strength of unidirectional metal matrix composite

A trial to predict the influences of ductility of matrix, interfacial bonding strength, and volume fraction of fiber on the tensile strength of unidirectional metal matrix composites was attempted by means of a Monte Carlo computer simulation method. The main results are summarized as follows. (1) The strength of strongly bonded composites increased with increasing ductility of matrix and then remained nearly constant. (2) When the matrix was ductile, the strength of composite increased with increasing interfacial bonding strength and then remained nearly constant. When the matrix was not ductile, the strength increased but then decreased with interfacial bonding strength. In this case, there was an optimum bonding strength, for which the strength of composite was highest. (3) Concerning the strength of composite as a function of volume fraction of fiber, there arose the case where it is approximately described by the rule of mixtures and also the case where it is not described by this rule, depending on the ductility of matrix, interfacial bonding strength, and scatter of strength of fiber.     

Interfacial characteristics for brazing of aluminum matrix composites with Al-12Si filler metals

Discussions concerning the interfacial reactions and characterizations in brazing aluminum matrix composites are documented in this study. Joints of alumina particulate reinforced 6061 aluminum matrix composites were made using an Al-12 (wt pct) Si filler metal by vacuum brazing. The resulted maximum bonding strengths were 75.4, 81.5, and 71.8 MPa for 10, 15, and 20 vol pct alumina reinforcement, respectively. The microstructural examinations revealed that the bonding strength was strictly related to the reinforced alumina particles and the reaction products presented at the joint interfaces. During brazing, Mg segregated at the joining interface and alumina/6061 Al interface. Further, reactions between alumina and 6061 Al matrix resulted in the formation of Mg-rich phases, such as MgAl₂O₄ and MgO, near the joining interface and the alumina reinforcement. The Si in the filler material penetrated into the metal matrix composites (MMCs) matrix and segregated at the alumina/6061 Al interfaces. This phenomenon can be confirmed by a joint between two alumina bulk specimens.     

Surface Characteristics of Rare Earth Treated Carbon Fibers and Interfacial Properties of Composites

Effect of rare earth treatment on surface physicochemical properties of carbon fibers and interfacial properties of carbon fiber/epoxy composites was investigated, and the interfacial adhesion mechanism of treated carbon fiber/epoxy composite was analyzed. It was found that rare earth treatment led to an increase of fiber surface roughness, improvement of oxygeaa-containing groups, and introduction of rare earth element on the carbon fiber surface. As a result, coordination linkages between fibers and rare earth, and between rare earth and resin matrix were formed separately, thereby the interlaminar shear strength （ILSS） of composites increased, which indicated the improvement of the interfacial adhesion between fibers and matrix resin resulting from the increase of carboxyl and carbonyl.     

Prevention of intellectual disabilities: early interventions to improve cognitive development

The isothermal enthalpy changes with time of a dental composite were examined by microcalorimetry to isolate the effects of different filler concentrations and curing times on chemical aging of these composites. Urethane dimethacrylate (UDMA) monomer, zirconia-silica (ZS) powder, and 3-methacryloxypropyltrimethoxysilane (MAPM) were used as organic and inorganic matrices, and a coupling agent, respectively. The composite was mixed in different ratios and cured by visible light. The enthalpy changes with time for 0, 15, 45, 75% ZS-filled UDMA and 75% MAPM-silanated ZS-filled UDMA cured for 13, 30, 90, 150, and 300 s were measured at 37.0 degrees, 57.0 degrees, and 65.5 degrees C until equilibrium. Increased curing time and filler concentration caused the excess enthalpy changes (dH) and their rate of change (dH/dt) to increase with annealing time and apparent equilibrium was reached faster. In addition, dH showed nonlinear dependence with the increase in filler concentration by showing a maxima for samples containing 25 wt% filler. Further, filler silanation caused dH/dt to increase and required shorter times to reach apparent equilibrium. dH also reached a minimum when samples contained silanated filler, compared to composites containing unsilanated filler. It was concluded that the shorter curing time caused the occurrence of spontaneous densification, which facilitated continual resin curing; and longer curing time caused higher crosslinking of the organic phase. Moderate concentration of inorganic phase restricts the molecular motion of the surface layer of polymer onto filler particles, and the polymer is regarded as highly crosslinked, while a higher filler concentration forms aggregates that are covered by the polymer which causes a decrease in the molecular packing of the resin, and is reflected as low enthalpy values. Finally, silanation of the filler showed a highly endothermic reaction that is probably due to breaking and forming of bonds at the interface between the organic and the inorganic phases in the composites.     

Composite biomaterials with chemical bonding between hydroxyapatite filler particles and PEG/PBT copolymer matrix

In an effort to make composites from hydroxyapatite and a PEG/PBT copolymer (Polyactive 70/30), chemical linkages were introduced between the filler particles and polymer matrix using hexamethylene diisocyanate as a coupling agent. Infrared spectra (IR) and thermal gravimetric analysis (TGA) confirmed the presence of Polyactive 70/30 on the surface of HA filler particles. The amount of chemically bound polymer was 4.7 wt.%, as determined by TGA. The mechanical properties of the composites, that is, tensile strength and Young's modulus, were improved significantly by the introduction of a chemical linkage between the filler particles and polymer matrix compared to control composites. This method provides an effective way to introduce chemical linkage between HA filler particles and a polymer matrix. By optimizing the grafting process, a further improvement of the mechanical properties in the composites can be expected.     

宏观颗粒增强铁基复合材料的制备与性能

颗粒与基体之间难以均匀稳定的混合以及二者的界面结合强度较差是限制颗粒增强金属基复合材料制备以及推广应用的共性关键问题,而目前的主要解决措施"预制体法"以及"润湿化预处理技术"又存在生产效率较低、制备成本较高等问题.基于此,在液态模锻的基础上,提出了不做预制体、也不进行润湿化预处理的制备颗粒增强金属基复合材料的新技术——"随流混合＋高压复合"技术,并采用此方法成功制备了复合效果良好的ZTA/KmTBCr26抗磨复合材料.研究了ZTA/KmTBCr26复合材料的微观组织、硬度以及冲击性能,发现复合材料内部颗粒分布比较均匀,颗粒与KmTBCr26基体的结合紧密,属于微机械啮合.冲击试验结果表明,复合材料的冲击韧性与单一金属基体相比显著降低,冲击断口形貌显示材料的断裂是沿颗粒内部扩展的,没有出现颗粒的整体脱落,说明陶瓷颗粒与金属基体具有比较高的结合强度.考察了ZTA/KmTBCr26复合材料与单一KmTBCr26的干摩擦磨损性能,结果表明,低载荷条件下ZTA/KmTBCr26复合材料的磨损性能是KmTBCr26的1.82倍,而高载荷条件下复合材料的磨损性能则是KmTBCr26的3.3倍.      

Effect of rare earths surface treatment on tribological properties of carbon fibers reinforced PTFE composite under oil-lubricated condition

The effect of rare earths （RE） surface treatment of carbon fibers （CF） on tribological properties of CF reinforced polytetrafluoroethylene （PTFE） composites under oil-lubricated condition was investigated. Experimental results revealed that RE treated CF reinforced PTFE （CF/PTFE） composite had the lowest friction coefficient and wear under various applied loads and sliding speeds compared with untreated and air-oxidated composites. X-ray photoelectron spectroscopy （XPS） study of carbon fiber surface showed that, after RE treatment, oxygen concentration increased obviously, and the amount of oxygen-containing groups on CF surfaces were largely increased. The increase in the amount of oxygen-containing groups enhanced interfacial adhesion between CF and PTFE matrix. With strong interfacial adhesion of the composite, stress could be effectively transmitted to carbon fibers; carbon fibers were strongly bonded with VITE matrix, and large scale rubbing-off of PTFE be prevented, therefore, tribological properties of the composite was improved.     

Evaluation of Tribological Performance of PTFE Composite Filled with Rare Earths Treated Carbon Fibers under Water-Lubricated Condition

Carbon fibers （CFs） were surface treated with air-oxidation, rare earths （RE） after air-oxidation, and rare earths, respectively. Erichsen test was conducted to study the interfacial adhesion of PTFE composites filled with carbon fibers treated with different treatment methods. Tribological properties of the PTFE composites, sliding against GCr15 steel under water-lubricated condition, were investigated on a reciprocating ball-on-disk UMT-2MT tribometer. The worn surfaces of the composites were examined using scanning electron microscopy. Experimental results reveal that RE treatment is superior to air oxidation in promoting tribological properties of CF reinforced PTFE （CF/PTFE） composite. The friction and wear properties of PTFE composite filled with RE treated CF are the best of the PTFE composites. RE treatment is more effective than air oxidation to improve the tribological properties of CF/PTFE composite owing to the effective improvement of interfacial adhesion between carbon fibers and PTFE matrix.     

Modification of the interface in SiC/Al composites

Methodologies both to avoid the formation of Al₄C₃ and to tailor the interfacial structures in a SiC/2014 Al composite were demonstrated. Modification of the interfacial structures in the SiC/2014 Al composite was made by forming SiO₂ layers on the surfaces of SiC via passive oxidation at elevated temperatures. In the 2014 Al composite reinforced with the oxidized SiC, MgAl₂O₄ and Si crystals were observed to be present at the interfacial region as a result of the reaction between the SiO₂ layer and the matrix. On the other hand, in the case of the 2014 Al composite reinforced with unoxidized SiC, SiC was found to react with the Al matrix to form both Al₄C₃ and Si. Qualitative measurements of the interfacial bonding strength were carried out on composites having various types of interfaces and thicknesses. Detailed interfacial structures and phase identifications, which were examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM), were presented.     

Mechanical Properties and Dry Sliding Wear Behaviour of Molybdenum Disulphide Reinforced Zinc–Aluminium Alloy Composites

ZA-27 alloy is a lightest alloy which offers excellent bearing and mechanical properties in automobile and industrial applications. In this study, the MoS₂ particles with 0.5, 1 and 1.5 (wt%) weight percentages were reinforced in ZA-27 alloy to form composites, which were fabricated by using ultrasonic assisted stir casting method. The ZA-27/MoS₂ composite specimens were examined for chemical composition with the aid of XRD technique and EDS. Microstructure analysis of the ZA-27/MoS₂ composites was studied using SEM. Tests were conducted for mechanical properties such as tensile strength and hardness on ZA-27/MoS₂ composites samples as per ASTM standards. Dry sliding wear behavior of the composites was tested at various operating conditions by using pin-on-disc apparatus. Microstructural images of the ZA-27 composites reveal that there is a uniform dispersion of the MoS₂ particles in the base material. From the results it is observed that the mechanical properties increases with ZA-27 reinforced with 0.5 wt% MoS₂ composite and further decreases with increase in the filler content. The enhanced wear resistance is observed in ZA-27 reinforced MoS₂ composites as compared to the unreinforced alloy. The wear rate of the ZA-27 composites decreases with the increase in filler content, further the worn surfaces as examined using SEM reveals the wear mechanism explaining the improved wear resistance of the particulate composites.     

混料时间和挤压对SiC增强纯Al基复合材料显微组织和力学性能的影响

采用粉末冶金法制备SiC颗粒增强工业纯Al基复合材料,研究混料时间和挤压对复合材料显微组织和力学性能的影响。研究表明:机械混粉过程存在最佳的混料时间,混料时间为16 h时SiC颗粒分布均匀,复合材料的密度高、力学性能好。挤压可以改善复合材料的界面结合强度、减少孔洞的数量,从而提高材料的致密度和力学性能。烧结态复合材料的断裂机制以基体的脆性断裂以及增强相与基体的界面脱粘为主。挤压态复合材料的断裂以基体的韧性断裂以及SiC颗粒的脆性断裂为主,伴随着少量的基体与SiC颗粒的界面脱粘。     

Fiber-Matrix interactions in brittle matrix composites

Brittle matrix composites, including carbon-carbon (C-C) and ceramic matrix, offer a new dimension in the area of high-temperature structural materials. Fiber-matrix interactions determine the mechanism of the load transfer between the fiber and matrix and resulting mechanical properties. Composites studied in this work include a C-C composite densified with a chemical vapor infiltration (CVI) pyrolytic carbon, silicon carbide fiber-silicon carbide matrix composite, and carbon fiber-silicon carbide matrix composites densified by the CVI technique. The type of the interfacial carbon in C-C composites was found to control their mechanical properties. The presence of the compressive stress exerted by the matrix on the carbon fibers was attributed to an increase in flexural strength. The transverse matrix cracking in C/SiC composites was believed to cause a lowering in the flexural strength value. Brittle fracture behavior of SiC/SiC composites was correlated with the presence of an amorphous silica layer at the fiber-matrix interface. This invited paper is based on a presentation made in the symposium “Structure and Properties of Fine and Ultrafine Particles, Surfaces and Interfaces” presented as part of the 1989 Fall Meeting of TMS, October 1–5, 1989, in Indianapolis, IN, under the auspices of the Structures Committee of ASM/MSD.     

Ascending Order of Enhancement in Sliding Wear Behavior and Tensile Strength of the Compocast Aluminum Matrix Composites

The emerging demand of light weight alloys and composites for the engineering and structural applications leads to explore the possibility to develop new techniques to achieve materials of high performance. In the present study, Al–B₄C reinforced composite has been developed via semi solid technique. The influence of Boron carbide (B₄C) content on the dry sliding wear characteristics of Al6061 matrix composites has been assessed using a pin-on-disc wear test. Wear rate was found to increase in ascending order with B₄C particles content. On comparing the wear rate, it has been found that the wear resistance offered by coated B₄C reinforced Al 6061 alloy matrix composites is higher than both base Al alloy and uncoated composites with incorporation of harder phase. This shows the good interfacial bonding of coated B₄C and Al6061 alloy matrix phase.     

WC_p/2024铝合金复合材料界面反应的分析

采用真空热压法在不同温度下制备了体积分数为12%的WCp/2024Al复合材料,试验中所用WC原始粉末的平均粒径分别为2μm和8μm.利用XRD、SEM、EDS等方法对增强颗粒与基体金属之间的界面反应进行了研究.结果表明,界面反应的主要产物为WAl12,但是当制备温度较高时,界面反应产物中出现少量Al5W,并且WCp(2μm)/2024Al复合材料界面反应的起始温度低于WCp(8μm)/2024Al复合材料.硬度测试结果表明,界面反应发生后,复合材料的硬度提高,最高比例达50%.     

Tailoring interfacial shear strength of SiC fiber-reinforced brittle matrix composites

The interfacial shear strength of Nicalon SiC fiber-reinforced glass-ceramic matrix composites was aimed to be tailored via two methods: (1) varying of the thickness of the carbon-rich interfacial layer between the fiber and the matrix by controlling hot pressing period and (2) formation of the secondary interfacial layer, TaC, at the carbon/matrix boundary by doping the Ta₂O₅ matrix addition. In the series of composites with varying carbon-rich layer thickness, fiber/matrix debonding mostly occurred at the carbon/matrix boundary and hence the increase in the carbon-rich layer thickness did not cause any apparent changes in the interfacial shear strength. In the TaC formed series of composites, the interfacial shear strength was affected considerably by the presence of the TaC phase at carbon/matrix boundary. The Ta₂O₅ addition to control the quantity of the TaC phase has shown to be a useful method to tailor the interfacial shear strength of SiC fiber/glass-ceramic composites.     

纤维类型和涂层对纤维增强MoSi2复合材料弯曲性能的影响

以短切碳纤维(Cf)和碳化硅纤维(SiCf)为增强相,并用化学气相渗透法对部分纤维进行炭涂层处理,采用热压法制备了4种纤维增强MoSi2基复合材料(SiCf-MoSi2、SiCf/C-MoSi2、Cf-MoSi2和Cf/C-MoSi2),研究了纤维类型及表面炭涂层对MoSi2基复合材料弯曲性能的影响.结果表明纤维的加入明显提高了MoSi2的抗弯强度,加入5%SiCf和5%Cf的复合材料的强度比纯MoSi2分别提高了9.0%和22.8%,Cf增强作用明显优于SiCf;纤维类型相同时,具有炭涂层的纤维增强效果更显著,5%Cf/C-MoSi2复合材料的强度最高,达到了364.7MPa,比纯MoSi2的强度提高了30%;扫描电镜分析表明,无炭涂层的SiCf与MoSi2基体间存在着明显的裂缝,炭涂层改变了纤维与基体的界面结合;有涂层纤维的断裂机制为首先脱粘然后拔出.     

Correlation of tensile strength with fracture modes of KAOWOOL- and SAFFIL-reinforced 339 aluminum

The tensile strengths of composites of 339 aluminum reinforced with either SAFFIL or KAOWOOL fibers are compared over the temperature range of 20 °C to 300 °C. For this type of composite, in which the discontinuous fibers are randomly oriented, the fibers perpendicular to the applied stress play a critical role, which in turn creates a dependence upon the interfacial bond strength. The KAOWOOL fibers form a strong interfacial bond so that tensile failure occurs either in the matrix at 300 °C or by fiber cleavage at 20 °C. In the T5 condition, the SAFFIL interface is weaker than the matrix alloy so that failure occurs by delamination of the transverse fibers. Thus, although the SAFFIL fibers are 40 pct stronger than the KAOWOOL fibers, the T5 composites have the same ultimate tensile strengths. A T6 heat treatment promotes an interfacial reaction with magnesium. This strengthens the SAFFIL interface so that failure occurs primarily in the matrix, producing higher composite strengths. The reaction with the KAOWOOL fibers is so extensive that the matrix, and therefore the composite strength, is drastically decreased. When account is taken of the different fracture modes, together with the matrix strengths as determined by nanoindentation, the calculated values of composite strength are in good agreement with experiment.